Short answer: it depends on .... ???
There is no short answer - in our company (which does non-platform-specific consulting) we experienced that the main advantages are QV's
# flexibility in adhoc-reporting
# short implementation cycles and hereby lower project costs
Otherwise we have to say that QV is somewhat "weak" in
# standard-reporting and publishing in terms of export formats and control
Also we think, that QV11's new features like collaboration, comparative analysis and user-customizable charts are "killer-features".
If a customer wants standard-reporting he is better off with "traditional" BI-tools, if he wants analysis and flexibility, he is best with QV ;-)